Some people are just naturally scared of dogs. And they've been teased about their fear since Childhood. Their friends pick on them any time a dog is around. And it's a self fulfilling fear because dogs can smell and sense your fear which makes them nervous and untrusting of you which makes you even more fearful of them.
So when they see a dog get put down like this it makes them feel good. It's comforting for them to see other grown men with the same irrational fear. They feel justified themselves, so they justify any actions of the police.
